Body-wearable direction finder
Soyka (Russian: Сойка) is a Russian wide-range body-wearable
intercept receiver that was used for locating clandestine
radio stations and intercepting communication between agents.
It was developed in the USSR and was
used during the Cold War by most countries of the Warsaw Pact.
Like other secret Russian equipment, it was named after a bird.
Soyka is the Russian word for jay.
An alternativename for the receiver is
(Russian: Сова) which is
the Russian word for owl. 1
Soyka consisted of a main unit and several accessories and
plug-in units, packed together in a small suitcase.
The image on the right shows the main unit as it was used
by the East-German intelligence service (Ministerium für
in the former DDR, hence the German labels covering the
The shape of the main unit is curved, to allow the receiver to
be hidden under the operator's clothing. All connections are
at the top panel.
Frequency plug-in and adjustement is also at the top
(more about plug-in units below).
Also on the top panel are the antenna sockets: one for a wire
antenna and one for a loop antenna. The latter has been modified
by the Stasi for use with (western) BNC connectors. A suitable
loop antenna, that can be hidden under
the clothing, is also supplied with the set.
The other sockets are for power (9В),
and headphones (ТЛФ).
All sockets are of the same type.
The receiving frequency can be set by adjusting a
around the frequency plug-in unit, whilst a separate
recessed fine tuning knob
is available to its right.
A small light can be turned on in
order to read the frequency scale in the dark.
The radio featured here is commonly known as Soyka (Сойка),
but some websites identify it as Sova (Сова). Although it is
possible that the receiver was known under different names
— it was used by different USSR departments —
it is likely that Sova was another version of this receiver,
or a different receiver altogether.
The receiver has a large number of controls and connections. The controls
are spread over the top panel and the front panel of the unit, in such
a way that they can be accessed by the operator when the receiver is worn
on the chest using the supplied leather belt.
The image below shows the receiver as it is seen by the operator,
with its top panel at the bottom.
Two antenna sockets are present on the top panel, allowing three types of
antenna to be connected. The leftmost socket is used for an omni-directional
antenna that can be used for interception of agent communication or
to search for a certain signal or station.
For direction finding, the rightmost socket is used. It can be used for a
directional body-worn loop-antenna, or a V-antenna
consisting of two wires that are hidden in the operator's sleeves.
In normal operation, the V-antenna is used as a dipole and a slide switch
just below the fine tuning knob (marked o - ∞) can be used to select
the required antenna radiation pattern. When set to ∞ it is suitable
for direction finding and can be used to find the minimum signal strength.
The receiver has a built-in HF pre-amplifier that can be bypassed with the
Near/Far switch when in close proximity of the transmitter. In direction
finding operations, the sentivity of the receiver can be adjusted with a
potentiometer (RF Gain).
Furthermore, the bandwidth of the receiver can be adjusted
wth the Wide/Narrow switch.
The MODE-switch is used to select the required mode of operation.
The user can select between:
- ТЛГ. 1 (TLG, Telegraphy)
This mode is used when listening to telegraphy signals like
morse codes (CW).
The CW tones are heard through the speaker.
- ТЛФ (TLF, Phone}
This mode is used for the reception of phone signals (AM) that are used for
voice conversations. The demodulated speech is heard through the speaker.
- ТЛГ. 2 (TLG, Telegraphy with Tone)
In this mode an LF signal is injected directly at the antenna input
allowing all types of signal, including silent carriers, to be traced.
A continuous 8 kHz tone is heard through the speaker. The stronger the
signal, the louder the tone.
The complete set is packed into a small unobtrusive cheap-looking
suitcase, complete with all accessories, plug-in units and
batteries. The case measures just 46 x 30 x 14 cm and is made of
green and yellow leather. At the time it could be used to travel
The image on the right shows a typical Soyka configuration
packed in the original suitcase. It contains several 'slots'
in which a rigid boards with canvas pockets are located.
At the far right is the leather belt,
used for carrying the
Soyka around the waist, and the Power Supply Unit.
Inside the case are several brown canvas pockets containing the
accessories and plug-in units. The actual Soyka unit itself is
packed in yet another canvast pocket and is not visible in the
image as it is 'face down' in the rearmost slot.
A special small pocket
is supplied to allow three spare plug-in
units to be hidden under the clothing whilst operating the
Various antennas, such as a loop antenna and a simple wire antenna,
are supplied for a variety of applications.
The loop antenna, hidden in green cloth, can be hidden under the
cloting as well.
Unlike other Russian body-wearable direction finders, like
Sinitsa, the suitcase of the Soyka does not contain
It is therefore very difficult to identify the correct location
of each item and to determine whether a set is complete or not.
Here is an attempt:
The drawing above shows the layout of the suitcase if everything is
packed correctly. There are two rigid boards that can be removed from
the suitcase. Each board hold canvas pockets at either side. The board
at the rear is stored horizontally with the receiver stored at the
bottom side (not visible here). The board at the front is stored vertically
and is retained by two rigs in the frame inside the suitcase.
- Receiver (main body unit)
- Chest belt
- Plug-in coils 1-12 (probably less with earlier version)
- Wire antenna
- Loop antenne
- Large battery holder (for 2 x 4.5V)
- 2 x Rechargeable 9V battery (cylinder)
- 2 x Small 9V battery holder (cylinder, not present with earlier version)
- Power supply/battery charger
- Volt meter
- Extra pouch for spare coils (not with earlier version)
Soyka was suitable for a wide frequency range (0-30 MHz),
divided over several bands. For each band, a separate plug-in
coil is available. Two special coils are supplied for
non-selective wide-band operation (indicated with a * below).
The following plug-in units were available:
- 0.7-1.1 MHz
- 1.1-1.7 MHz
- 1.7-2.6 MHz
- 2.6-4 MHz
- 4-6 MHz
- 6-9 MHz
- 9-13 MHz
- 13-18 MHz
- 18-24 MHz
- 24-30 MHz
- 3-15 MHz *
- 1-30 MHz *
All plug-in units have the same physical
size. They consist of a metal cylinder of approx. 42 mm,
with a diameter of 21 mm. The frequency scale is at the top, whilst
the contacts are at the bottom.
Inside a plug-in unit is a tuned circuit, consisting of a series
of capacitors and coils.
The plug-in is held in place by a lock that is operated
with a small handle at its side.
Please note that the
plug-in can only be removed when
the frequency dial is
in a certain position.
A plug-in unit can easily be opened by removing the rigged
bolt at the top.The frequency scale then comes off and the
unit can be taken out of its protective metal cylinder.
The image on the right shows the interior of plug-in unit #1.
It can be adjusted by inserting the tuned circuit inside
a special cylinder with 4 holes.
This also requires the Soyka receiver itself to be opened.
last two plug-in units
(XI and XII, or 11 and 12) are special.
They can be used to convert the receiver into a wide-band
non-selective receiver, ideal for picking up transmitters operating
on unknown frequencies in the immediate vicinity.
This would also work with transmitters that use Frequency Hopping (FH).
As a result, the receiver loses its sensitivity, which is a desired
side-effect, as broadcasting stations would otherwise interfere with
the reception of the local signal.
The Soyka main unit is powered by a 9V source, which should be
connected to the leftmost connector on the top panel (9В).
It can be powered by a variety of sources, all of which are
included with the unit. The first possibility is the
that is supplied with the kit. The same PSU is also used to
charge the NiCd batteries (see below).
Alternatively, the unit can be powered with a
cylindrical 9V NiCd pack,
of which two are supplied with the unit.
As the cells of our device had already started leaking, we had to
As a last resort, another metal cylinder with a small 9V
block battery can be used, but it lasts only a short period
For sustained portable use, the unit can best be powered
by two 4.5V flat batteries. A special
battery holder with
a suitable connector is supplied with the set. It is shown
in the image on the right, where two Varta batteries are
Soyka receivers were also used in the former DDR (East-Germany) by the
Ministerium für Staatssicherheit (MfS, Ministry for State Security)
better known as the Stasi. It was the main organisation for espionage
in the DDR and was actively involved in tracking down agents.
As the typical Russian antenna sockets were in short supply in the DDR,
the socket that was used the most has been replaced by a standard BNC socket.
The antennas for this socket have been modified with BNC plugs accordingly.
The image on the right show a Soyka receiver that was found in the Stasi
headquarters near Berlin, just after the fall of the Berlin Wall in 1989.
Pieces of paper with German translations are taped over the original
On the international forums there seems to be some confusion about the name
of this intercept receiver. Although the unit is commonly called Soyka
(Сойка), there are some that suggest that this name was only used by
the KGB and other secret services, while everyone else called it Sova
(Сова). Another possibility is that Sova is an earlier variant of the
later Soyka, probably with a smaller frequency range and fewer plug-in coils.
If you know more, please let us know.
- Paul Reuvers and Marc Simons, Soyka portable intercept receiver
Crypto Museum, Investigation August 2011.
- Louis Meulstee, USSR Portable Intercept Receivers
Wireless for the Warrier. Volume 4. September 2004. ISBN 0952063-36-0.
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© Crypto Museum. Created: Monday 03 August 2009. Last changed: Tuesday, 26 September 2017 - 07:32 CET.